Optical access network is generally evolving from the broadband passive optical network (B-PON), Gigabit Passive Optical Network (G-PON) and Ethernet Passive Optical Network (E-PON) based on the TDM technology to the NG-PON with multiple wavelengths and high speed based on the combination of the TDM and WDM technologies. Two-way high-speed transmission with multi-wavelength single optical fiber between the optical line terminal (OLT) and the optical network unit (ONU) significantly improves the optical fiber utility.
For the G-PON, the upstream and downstream transmission optical spectrum ranges of the current TDM-PON are specified respectively as that, the range of the downstream S band λs is 1480 nm˜1500 mm, and in order to coexist with the NG-PON, the range of the upstream O band λo is 1290 nm˜1330 nm. ITU-T optical access network G.984.5 mentions that the OLT in the existing TDM-PON is called the legacy OLT, and its working band is the basic band λo+s. The OLT in the NG-PON is called the Upgrade OLT. The full service access networks (FSAN) organization specifies the wavelength of the NG-PON, the range of whose upstream wavelength is 1260 nm˜1280 nm, and the range of whose downstream wavelength is 1575 nm˜1580 nm, and it also specifies that the wavelength range of the CATV downstream signal is 1550 nm˜1560 nm.
In order to implement the architecture for the TDM-PON to smoothly upgrade into the NG-PON system or to be compatible with the NG-PON system, wavelength division multiplexing 1 (WDM1, G.984.5 specifies that the name of the wavelength division multiplexer for making the NG-PON compatible with the existing time division multiplexing PON is WDM1) should be inserted between the legacy OLT, the upgrade OLT and the splitter to make the existing TDM-PON and the NG-PON transmit optical signals in different bands with a single optical fiber in the same optical distribution network (ODN), as shown in FIG. 1. WDM1 can make the ODN in the existing TDM-PON transmit the NG-PON optical signal to achieve the smooth upgrading from the TDM-PON to the NG-PON.
Since WDM1 requires high optical signal working band isolation, low optical network insert loss, high practicality, and high performance to price ratio, there is no scheme to implement the WDM1 device module in the prior art.